"The mystery has been solved?"

"It has," replied Lord Hastings quietly.

"And you can suggest means for overcoming it?"

"I can," replied Lord Hastings, and added: "At the proper time and
place."

Von Rosten sat down and indicated Davis.

"Then you can vouch for this man?" he asked.

"Yes," replied Lord Hastings. "And I should be glad if you would release
him. He is a traitor to his country and something of a bungler, but I
can make use of him."

"Very well, sir," returned Von Rosten. "Then I shall turn him over to
you."

"If you would be so kind," said Lord Hastings.

The German again summoned his first officer.

"Take the irons off this man," he commanded.

The first officer motioned for Davis to follow him.

"Return when you have been released," ordered Lord Hastings.

"Very well," said Davis.

He left the cabin.

"Now," said Lord Hastings to Von Rosten, "I would be glad if you could
do a further favor for me?"

"Consider it granted if it is within my power," said the young German.

"Thanks," said Lord Hastings. "I should like to borrow half a dozen of
your crew. As you know, I am short handed, and I have work to do."

The German hesitated, but only for a moment.

"Very well, sir," he returned. "I shall be glad to let you have them.
Would you also wish me to take care of your British prisoners?"

"Oh, no," replied Lord Hastings with a gesture. "They are hard workers,
with a little urging," and he smiled. "They may come in very handily."

"As you please," replied the German.

A third time he summoned his first officer.

"Pick twelve men of the crew and have them ready to go aboard the U-16
with Captain Bernstorff here," he commanded.

The officer saluted and withdrew.

"Now, is there anything further I can do for you?" asked Von Rosten.

"Nothing, thank you," replied Lord Hastings, "and, with your permission,
as soon as Davis is freed of his shackles and the men are ready, I shall
return to my own vessel. I have work to do."

The young German bowed.

Half an hour later Lord Hastings, Jack and Frank again trod the deck of
the U-16. Davis and a crew of twelve German sailors also were aboard.

"And now," said Lord Hastings, "having dispensed with the formalities,
it is time to get busy."

CHAPTER XV.

PLOTTING.

"Now," said Lord Hastings, "as soon as we have lost sight of our new
friend, Von Rosten, we shall take a little trip to Ostend anyhow."

"What for, sir?" asked